Pattern of British–Irish Ice Sheet advance and retreat: geochemical insights from an offshore transect

This multiproxy study combines sedimentology, foraminiferal analysis and offshore geophysical data with the first application of the osmium isotope system to three marine sediment cores from a transect off the coast of NW Scotland to understand the complex glacial history associated with the last British and Irish Ice Sheet. Sampled subglacial till facies are characterized by the absence of foraminifera, high 187 Os/ 188 Os values ( c . 1.5) and low Re abundances reflecting the input of glacially eroded terrestrial sourced radiogenic Os. The overlying proximal to distal glaciomarine mud facies yield glaciomarine foraminifera, lower 187 Os/ 188 Os values ( c . 1.2) and high Re abundances owing to glacial retreat and a reduction in radiogenic Os input. Furthermore, alternating lithologies within the grounding line complex are reflected in the 187 Os/ 188 Os records, indicating the sensitivity of the osmium-isotope proxy to more nuanced changes in ice sheet behaviour. The acoustic stratigraphy and seabed morphology of this transect suggest that the British–Irish Ice Sheet (BIIS) margin retreated eastwards, an interpretation that is supported by radiocarbon dates above the sampled diamicton units. The new 187 Os/ 188 Os records presented here detect oscillations of the ice margin during its overall eastward retreat, revealing new insights into the dynamics and temporal behaviour of the BIIS.